436 G. W. Tyrrell—Petrography of South Georgia. 
The sedimentary rocks in Mr. Ferguson’s collection are as follows: 
Between Slosarczyk Bay and Cape Disappointment there are found 
siliceous slates, and phyllites with vein-quartz and lenticles of 
erystalline limestone, in all respects similar to the types found in the 
Lower Division of the Cumberland Bay Series. Phyllites with quartz 
veins also occur on Cooper Island. In Slosarezyk Bay occurs a horn- 
felsed shale with peculiar clots of epidote, which is clearly associated 
with the epidotized rocks described later. 
The Gold Harbour rocks are mainly sedimentary and are of some 
interest. There is a hard, green, quartzitic arkose, composed of 
extremely angular grains of quartz and felspar in about equal 
quantities. ‘lhe felspar is mainly microperthitic orthoclase, with 
some microcline, and varies considerably in freshness, but the turbid 
altered fragments are dominant. There is a little scattered chlorite, 
and some fine-textured siliceous matter which acts as cement. The 
rock is clearly an arkose derived immediately from a granite. It is 
entirely unsheared, and its interest lies in the fact that it supplies 
an original material for the puzzling ‘‘sheared felspathic grits”, 
‘‘ augen-erits’’, and ‘‘ porphyroids’’ (Nordenskjold) described in the 
earlier paper.t Several of these rocks occur in Gold Harbour. Their 
mineral composition is identical with that of the arkose described 
above; but the quartz has been crushed down to a fine-grained 
granulitic paste, which forms the groundmass to numerous augen of 
felspar. The latter are outlined by dark, indefinite, wavy lines, 
consisting mainly of greenish micaceous material. Recrystallization 
has begun in the rock, resulting in the production of innumerable 
flakes of sericite interpenetrating with the quartz of the groundmass. 
T'wo specimens from Gold Harbour are probably sheared acid tuffs, 
somewhat similar to those described in the earlier paper.” They are 
hard to separate from the sheared grits, but the augen texture is not 
so well developed, quartz is much less abundant, and the felspar has 
frequently not been aligned with the foliation. One of the rocks 
approaches a slate in appearance. The cleavage is interrupted by ° 
numerous augen of fresh orthoclase, and a few of oligoclase; and also 
by a few rock fragments, one of which is clearly a trachyte. This 
rock is therefore close to the trachytic tuffs described previously, 
although it appears to contain more sedimentary material than they. 
Finally a phyllite interbedded with grits, and a coarse conglomeratic 
quartzite rock impregnated with pyrrhotite, may be noticed from Gold 
Harbour. ‘The latter rock contains a large quantity of chlorite inter- 
leaved with brown biotite, and has the appearance of having suffered 
thermal metamorphism. All the above-described rocks probably belong 
to the Lower Division of the Cumberland Bay Series. 
The igneous rocks may be classified as follows: (1) Epidiorite ; 
(2) Ophitic dolerite and basalt; (8) Alaskite; (4) Quartz-felsite, with 
spherulitic and non-spherulitic varieties; (5) Lavas and tuffaceous 
rocks of doubtful affinities, and epidosite; (6) Augitite. 
1 Tyrrell, ‘‘ The Petrology of 8. Georgia’’?: Trans. Roy. Soc. Edinburgh, 
vol. 1, p. 825, 1915. 
2 Tbid., p. 827. 
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